This invention relates to ink jet printers. In particular, this invention relates to a novel design and method of manufacture of a thermal inkjet print head.
Thermal inkjet printers have become ubiquitous.
These printers typically use semiconductor-based print heads which have individually-controlled ink-ejecting printing elements that heat water-based inks to vaporization. Vaporizing the ink causes it to be propelled onto a print media through microscopic holes formed in a plate or shield. Thermal energy to vaporize ink is supplied from electric current driven through small thin film resistors that are in thermal contact with ink, which is otherwise held in place within the print head by capillary effect.
Prior art thermal inkjet printers form images on print media by repeatedly passing a print head over the media. Small quantities of ink are xe2x80x9csprayedxe2x80x9d onto the paper by turning on and turning off the thermal ink jet printing elements as the print head moves across the paper or print media.
At least one problem associated with existing inkjet printers is the speed at which these printers can produce acceptable quality output levels. Because a finite time is required for ink droplets to traverse the distance between the media and the print head, there is an upper speed limit for the print head beyond which further speed increases are not possible. Instead of moving the print head across the media, a method and apparatus by which an entire line of a page might be printed at once could provide a significant overall printing speed increase.
A page-wide printer head formed from glass fiber nozzles onto which are deposited semiconductor heating elements, and current driving circuitry, can print an entire line of a single page at one time using thermal ink jet action. Narrow glass tube ink conduits are formed from hollow glass fibers which are sintered together, drawn to constrict the diameters of the hollow fibers and then longitudinally sliced to provide an array of glass tube nozzle assemblies. By using semiconductor processing techniques, heater resistors and control circuitry is formed onto the glass surfaces. The heater resistors are deposited into the interior of the hollow glass fibers where they are used to heat liquid-based ink and ink components to vaporization.
The current drive circuitry is comprised of transistor-controlled silicon controlled rectifiers (xe2x80x9cSCRsxe2x80x9d) deposited onto the print head. The SCRs drive current through the heater resistors deposited into the open ends of the glass fibers. Hundreds or even thousands of individual current drive circuits, each circuit being comprised of a pair of SCRs wired in a series fashion, are fired by a control pulses delivered to a control transistor for each drive circuit. The current drive circuits of the SCRs are wired in a totem pole arrangement such that successive drive circuits are addressed by successive pulses on only two control lines wired to all of the series connected drive circuits.
Predetermined individual SCRs are first latched xe2x80x9conxe2x80x9d in sequence by a predetermined pulse in a synchronous train of pulses that are applied to the drive circuits. Individual drive circuits can be turned on or left off, i.e. in the SCR""s non-conducting state. A single power pulse delivered to all of the drive circuits after the circuits are provided with the addressing pulse stream provides the electrical energy through the SCRs latched xe2x80x9con,xe2x80x9d to vaporize ink.